About a third of the CO2 released into the atmosphere by humans each year is absorbed by the oceans. This helps slow the rate of global warming but also increases ocean acidity, posing a serious threat to marine life. Cquestrate, which was advocated in Manchester by Tim Kruger, is a plan designed to combat both of these problems at once.

The idea is to convert limestone into lime (a process similar to those used in the cement industry) and to add the lime to the oceans. There, it reacts with CO2 dissolved in the water, converting it into bicarbonate ions. These chemical changes decrease the acidity of the water and enable the it to absorb more CO2 from the air, thereby helping to reduce planetary warming.

The basic chemistry of the Cquestrate plan looks good, though two key questions remain: whether it would be feasible to mine and process a sufficient volume of limestone to make a significant difference to ocean acidity and global warming; and whether it will ever be affordable to capture and store the CO2 produced during the manufacture of the lime.